The present invention relates to information terminal devices represented by portable telephones and LCD (liquid crystal display) devices used in them. In particular, the present invention relates to a reflection type LCD device using light incident from an observation side to display an image, and a semi-transparent type LCD device capable of using transmitted light obtained from light incident from a side opposite to an observation side and/or light incident from the observation side simultaneously or selectively to display an image.
Since the LCD devices are thin in size, light in weight and low in power consumption, they are used as display devices in a wide variety of information terminal devices such as notebook computers, personal digital assistants, portable telephones and digital cameras.
Unlike cathode-ray tubes or plasma display devices, the LCD device does not emit light itself, but displays an image or the like by controlling light quantity of light incident from the outside. Furthermore, multi-color image display becomes possible by equipping the LCD device with color filters of a plurality of colors as light control elements.
In such LCD devices, a liquid crystal layer is interposed between a pair of substrates (hereafter also referred to as “first substrate and second substrate”) and an electronic latent image is converted to a visible image by controlling the molecular alignment of liquid crystal composites included in the liquid crystal layer by means of an electric field applied to the liquid crystal layer.
The LCD devices are classified into a direct matrix type and an active matrix type on the basis of the drive scheme. In the current LCD devices, the active matrix type forms a main stream because high-definition fast image display is possible.
The active-matrix type LCD device has active elements (switching elements) represented by thin film transistors' for pixel selection on the first substrate or the second substrate, and has color filters respectively having three colors for color display on either the first substrate or the second substrate.
In the reflection type LCD devices, an image is displayed by using light incident from the observation side. In the semi-transparent type LCD devices, transmitted light obtained from light incident from a side opposite to an observation side and/or light incident from the observation side can be used simultaneously or selectively to display an image.
The LCD devices are not self-light-emission type. Therefore, it is necessary to visualize an electronic latent image by illuminating it with visible light and emit resultant light to an observation face as image light. LCD devices exposed to illumination light such as natural light (external light) given from the observation face side are called reflection type. LCD devices exposed to illumination light given from the side opposite to the observation face are called transparent type. LCD devices capable of being exposed to illumination light given from the observation face side and exposed to illumination light given from the side opposite to the observation face are called semi-transparent type (semi-transparent reflection type).
As for disclosure of such a conventional technique, for example, JP-A-2000-187220 can be mentioned. As for the liquid crystal alignment used in such LCD devices, there are a homeotropic alignment scheme using a liquid crystal material having negative permittivity anisotropy and a homogeneous alignment scheme using a liquid crystal material having positive permittivity anisotropy. From the viewpoint of response time, the homogeneous alignment scheme using a liquid crystal material having positive permittivity anisotropy is more advantageous in the same way as JP-A-2000-187220.
Since the semi-transparent type LCD devices described in JP-A-2000-187220 are asymmetric in the vertical or horizontal visual field angle characteristics, however, color tone deviation occurs in the vertical or horizontal visual field angle direction in color display. As a method for solving this problem, there is a technique of dividing the alignment into a plurality of domains in a pixel and averaging visual field angle characteristics in respective domains to make the vertical or horizontal visual field angle characteristics symmetrical. As for disclosure of such a conventional technique in a transparent type LCD device that uses the homogeneous alignment scheme using a liquid crystal material having positive permittivity anisotropy and that has no reflection display function, for example, JP-A-2002-72209 can be mentioned.